Ovarian carcinoma is the leading cause of death from gynecological malignancies in the western world. Its high death rate is a result of the fact that most patients (~75%) are diagnosed at an advanced stage of disease with disseminated intra-abdominal metastasis. Debulking surgery followed by platinum-based chemotherapy schemes is considered standard care for these patients. However, despite an initial response rate of 65%-80% to first-line chemotherapy, most ovarian carcinomas relapse. Acquired resistance to further chemotherapy is generally responsible for treatment failure, resulting in an overall 5-year survival rate of only about 25% for late- stage ovarian cancer. Thus, there is urgent need to identify novel molecules that are responsible for chemoresistance and ovarian cancer development, and thus lead to new targeted therapy. MicroRNAs (miRNA) are a class of small RNAs that are phylogenetically conserved and play important roles in the regulation of cell survival, proliferation, differentiation and angiogenesis. Accumulated studies shows that miRNAs are frequently deregulated in human malignancy and function as either oncogenes or tumor suppressor genes. In addition, miRNA expression signatures correlate well with specific clinical cancer characteristics and can be used to classify normal and cancerous tissues as well as subtype of malignancy. Our preliminary data show frequent upregulation or downregulation of miRNAs in human ovarian cancer, some of which, especially miR-214, are involved in chemoresistance and metastasis and have oncogenic activity. Based on these preliminary data and the fact that each miRNA negatively regulates hundreds of genes, we hypothesize that miRNAs play significant role in ovarian carcinogenesis, intra-abdominal dissemination and chemoresistance and could be therapeutic targets for human ovarian cancer. Thus, the objective of this project is to determine the miRNAs as pathogenetic factors and therapeutic targets in ovarian cancer. To test our hypothesis and achieve our goal, we will 1) determine the mechanism of overexpression of miR-214 in ovarian cancer; 2) examine the effects of miR-214 gain- and loss-of-function on the neoplastic phenotypes of ovarian cancer cells and the oncogenic activity of miR-214 in OSE cells; 3) determine the consequence of miR-214 gain of function on ovarian tumorigenesis in transgenic mice and 4) validate the miR-214 targeted genes and determine the mechanism of miR-214 in oncogenesis.